Okay, hold on. Concerts of contemporary chamber music are supposed to be difficult, cerebral events, right? Attended by a handful of po-faced graybeards, half of whom sneak out at intermission? So what was with the packed house on Saturday night for Sybarite5, a string quintet that plays almost exclusively modern music? What was all that impassioned playing, those hard-driving rhythms, the blissed-out faces of the mostly young audience? And what about the cheering — the actual cheering — that filled the Sixth and I Historic Synagogue when the group returned onstage after intermission? Is this what modern music has come to? Genuine, spontaneous . . . excitement?

We can only hope. This cheerfully free-ranging ensemble (a string quartet, with added double bass) aimed its performance squarely at 21st-century ears, mixing new works from classical composers with Armenian folk songs, 1950s jazz by Dave Brubeck, the music of Radiohead, a bit of fluff from the pop band a-Ha, a snippet of Mozart and even an Argentinian tango or two. That kind of kitchen-sink eclecticism might sound a little contrived, but it made perfect sense in performance — maybe because of the visceral, even sensual expressiveness that the musicians of Sybarite5 brought to everything they played, and maybe because it was all — as violinist Sarah Whitney declared from the stage — “music we love.”

In a program of serial high points, there were too many to mention. Piotr Szewczyk’s jazzy “The Rebel” opened the evening and set its driving, fast-paced tone, and among the new “classical” works, Dan Visconti’s bluesy evocation of a train wreck (“Black Bend”) and Shawn Conley’s warmly pulsing “Yann’s Flight” were particular standouts. Violinist Sami Merdinian led the ensemble in three steamy, tango-infused works by Astor Piazzolla, while Brubeck’s “Blue Rondo à la Turk,” a movement from Mozart’s Divertimento in B flat, K. 137, and the fiery Romanian gypsy song “Turceasca” (by Taraf De Haidouks) kept things moving in clever, unpredictable directions.

Some of the most moving, luminous moments of the evening came during the late Pete Seeger’s “Where Have All the Flowers Gone?” But it was the endlessly fascinating music of Radiohead that seemed to be at the real heart of the concert, with deft arrangements by Paul Sanho Kim of “Paranoid Android,” “Weird Fishes” and “Motion Picture Soundtrack” that married the power of the originals with a classical sensibility. An intriguing and hugely enjoyable evening in every way — and a standout in the Washington Performing Arts Society’s fine winter season.